1. Field of the Invention
The present application relates to measuring devices, and more particularly, to articulated arm coordinate measurement machines for measuring coordinates in three-dimensions.
2. Description of the Related Art
Rectilinear measuring systems, also referred to as coordinate measuring machines (CMM's) and articulated arm measuring machines, are used to generate geometry information. In general, these instruments capture the structural characteristics of an object for use in quality control, electronic rendering and/or duplication. One example of a conventional apparatus used for coordinate data acquisition is a portable coordinate measuring machine (PCMM), which is a portable device capable of taking highly accurate measurements within a measurement sphere of the device.
Such devices often include a probe mounted on an end of an arm that includes a plurality of transfer members connected together by joints. The end of the arm opposite the probe is typically coupled to a moveable base. Typically, the joints are broken down into singular rotational degrees of freedom, each of which is measured using a dedicated rotational transducer. During a measurement, the probe of the arm is moved manually by a user to various points in the measurement sphere. At each point, the position of each of the joints must be determined at a given instant in time. Accordingly, each transducer outputs an electrical signal that varies according to the movement of the joint in that degree of freedom. Typically, the probe also generates a signal. These position signals and the probe signal are transferred through the arm to a recorder/analyzer. The position signals are then used to determine the position of the probe within the measurement sphere. See e.g., U.S. Pat. Nos. 5,829,148 and 7,174,651.
As mentioned above, the purpose of PCMM's is to take highly accurate measurements. As compared to stationary CMM'S, the challenge of taking highly accurate measurements is more difficult because PCMM's must also be portable, lightweight, and rugged so as to withstand the wear and tear associated with movement of the device. Accordingly, there is a continuing need to improve such devices. An example of a PCMM arrangement that has been successful can be found in U.S. Pat. No. 5,829,148 and the PCMM sold by ROMER under the tradename INFINITE® CMM. Such devices also advantageously provide infinite rotation about one or more joints of the device. In contrast, prior designs, carried wiring in the joint for transmitting power and signals to and from the probe and transducers. Although the wiring was flexible, the rotational freedom of the joints were restricted to prevent over-coiling. Infinite rotation eliminated the problem associated with the past designs. While the above references designs with infinite rotation have been successful, there is a general need to provide infinite rotation in a PCMM in a manner that can result in a decrease manufacturing and inventory costs while still maintaining and/or exceeding commercially required standards of accuracy.